Poly(alkylene carbonate) is an easily biodegradable polymer, and is useful as, for example, an adhesive agent, a packaging material, or a coating material. A method for preparing poly(alkylene carbonate) from an epoxide compound and carbon dioxide is highly eco-friendly in that phosgene, which is a poisonous compound, is not used and carbon dioxide is cheaply obtained.
Many researchers have developed various types of catalysts in order to prepare poly(alkylene carbonate) from an epoxide compound and carbon dioxide since 1960s. The present inventors recently disclosed a high-activity and high-selectivity catalyst synthesized from quaternary ammonium salt-containing Salen [Salen; ([H2Salen=N,N′-bis(3,5-dialkylsalicylidene)-1,2-ethylenediamine]-type ligand [Bun Yeoul Lee, Korean Patent Registration No. 10-0853358 (2008 Aug. 13); Bun Yeoul Lee, Sujith S, Eun Kyung Noh, Jae Ki Min, Korean Patent Registration No. 10-2008-0015454 (2008 Feb. 20); Bun Yeoul Lee, Sujith S, Eun Kyung Noh, Jae Ki Min, PCT/KR2008/002453 (2008 Apr. 30); Eun Kyung Noh, Sung Jae Na, Sujith S, Sang-Wook Kim, and Bun Yeoul Lee, J. Am. Chem. Soc. 2007, 129, 8082-8083 (2007 Jul. 4); Sujith S, Jae Ki Min, Jong Eon Seong, Sung Jae Na, and Bun Yeoul Lee, Angew. Chem. Int. Ed., 2008, 47, 7306-7309 (2008 Sep. 8)]. The catalyst disclosed by the present inventors exhibits high activity and high selectivity, and allows the preparation of a copolymer having a large molecular weight. Also, polymerization thereof is possible even at a high temperature, and thus, the catalyst can be applied in a commercial process. In addition, since a quaternary ammonium salt is contained in the ligand, the catalyst can be easily separated from the copolymer after a copolymerization reaction with carbon dioxide/epoxide and reused.
In addition, the present inventors carefully analyzed, particularly, the structure of a catalyst exhibiting high activity and high selectivity as compared with others among a catalyst group of the patent, and then found that the catalyst has a particular structure not known in the literature, in which a nitrogen atom of the Salen-ligand is not coordinated but only oxygen atoms are coordinated to a metal (see, Structure 1 below, Sung Jae Na, Sujith S, Anish Cyriac, Bo Eun Kim, Jina Yoo, Youn K. Kang, Su Jung Han, Chongmok Lee, and Bun Yeoul Lee, “Elucidation of the Structure of A Highly Active Catalytic System for CO2/Epoxide Copolymerization: A Salen-Cobaltate Complex of An Unusual Binding Mode” Inorg. Chem. 2009, 48, 10455-10465).

In addition, there was developed a method of easily synthesizing the ligand of Structure 1 above (Min, J.; Seong, J. E.; Na, S. J.; Cyriac, A.; Lee, B. Y. Bull. Korean Chem. Soc. 2009, 30, 745-748).
The compound of Structure 1, which is a highly-active catalyst, is used to prepare poly(alkylene carbonate) having a high molecular weight economically. However, since the glass transition temperature of poly(alkylene carbonate) is low (40° C. for poly(alkylene carbonate) prepared by propylene oxide and carbon dioxide) and the mechanical strength thereof is not high, there are certain limitations in developing usage of poly(alkylene carbonate).
As a way for overcoming these limitations of poly(alkylene carbonate), the present inventors developed and reported methods for preparing poly(alkylene carbonate) diol or polyol having a low molecular weight and also a plurality of —OH terminal groups and using the same for preparing polyurethane (Anish Cyriac, Sang Hwan Lee, Jobi Kodiyan Varghese, Eun Seok Park, Ji Hae Park, and Bun Yeoul Lee, Macromolecules 2010, 43, 7398-7401). Scheme 1 below shows a preparation mechanism of poly(alkylene carbonate) diol or polyol having a low molecular weight and a plurality of —OH terminal groups by the catalyst of Structure 1 above. Here, X− contained in the catalyst of Structure 1 above nucleophilically attacks epoxide coordinated with a metal, which is acting as a Lewis acid, thereby starting copolymerization of carbon dioxide/epoxide. When the polymerization reaction is started, growth of polymer chain from X− contained in the catalyst is started, and resultantly, X− becomes a polymer chain of which a terminal group is a carbonate or alkoxy anion. Here, when a (J(LH)c) compound containing an —OH group is introduced as a chain transfer agent in order to regulate the molecular weight, the carbonate or alkoxy anion takes protons contained in the (J(LH)c) compound to become an alcohol or carbonic acid type compound, and the J(LH)c compound becomes a carboxyl or alkoxy anion. Once the J(LH)c compound becomes the carboxyl or alkoxy anion, a polymer chain may grow therefrom. A proton exchange reaction rapidly occurs. Hence, the polymer material resultantly obtained by this proton exchange reaction and a chain growth reaction includes a polymer chain grown from X− contained in the initial catalyst and also a polymer chain grown from the J(LH)c compound introduced as a chain transfer agent. The molecular weight and chain shape of the polymer may be controlled depending on the amount and the structure of introduced chain transfer agent.

However, in the above Scheme 1, an organic alcohol compound or a carboxyl compound was used as the chain transfer agent. Further, it was not reported that a phosphorous compound is used as the chain transfer agent, to prepare poly(alkylene carbonate) having precisely controlled molecular weight and polymer chain structure. Further, it is not reported that a phosphorous compound is used as the chain transfer agent in a polymerization reaction of epoxide and carbon dioxide, to include a phosphate or phosphonate group in the polymer chain, thereby preparing a carbon dioxide/epoxide copolymer exhibiting flame-retarding property.